Root Plasticity and the Capture of Variable Rainfall by Desert Plants

在这个项目中，将研究沙漠植物的根的位置和行为与土壤水分可用性的变化有关，土壤水的可用性是此类干旱地区的限制因素。由于沙漠中的降雨只发生在很短的一段时间内，现有的根必须能够迅速吸收水分，或者植物必须能够产生新的高度吸收的根来应对这种降雨。此外，土壤在干旱期间不会均匀干燥，因为更潮湿的区域可能出现在土壤深处、岩石下或岩石缝隙中。因此，吸收水分的能力可以随根的长度而变化。在美国西南部索诺兰沙漠生长的植物的根将被检查，关于它们沿长度方向发生水分吸收的地方，是否在土壤较潮湿的部分形成特殊的根系特性，以及根是否在较潮湿的地区更多地分枝。这种检查将包括在田间进行各种浇水处理后对根进行挖掘，以及对接受不同水量的根的结构特征进行实验室调查。比较不同根构型植物的吸水特性。特别是，研究人员将检查龙舌兰的根，具有厚厚的储水叶子和不分枝的根(龙舌兰)，具有薄叶和不分枝的根的草(Pleuraphim Rigida)，具有粗茎和高度分枝的根的仙人掌(仙人掌)，以及具有薄叶和高度分枝的根的小灌木(Encelia Farinosa)。叶或茎厚的树种可以储存大量的水分，因此在干旱的早期阶段，根的反应可能与叶薄的树种不同。此外，根部容易分枝并在土壤较潮湿地区繁殖的物种将与根部相对不分枝的物种进行比较。将根据土壤深度的水分变化和季节差异，如降雨后和干旱期间的时间，来评估每一根的吸水能力。这将有助于解释目前沙漠中植物的分布情况，以及未来是否会随着气候变化而发生变化。由于土壤湿度的变化，沙漠植物的根系特性的变化也可以用来预测潮湿生境中的植物反应，那里的降雨量未来可能会出现更极端的波动。

In this project, the location and behavior of roots of desert plants will be examined with respect to variation in the availability of soil water, the limiting factor in such arid regions. Because rainfall occurs during only brief periods in the desert, existing roots must be able to take up water quickly or the plants must be able to produce new highly absorptive roots in response to such rainfall. Also, the soil does not dry out uniformly during drought, as wetter regions can occur deeper in the soil, under rocks, or in rock crevices. Thus, the ability to take up water can vary along the length of a root. Roots of plants growing in the Sonoran Desert of the southwestern United States will be examined with respect to where along their length water uptake occurs, whether special root properties develop in wetter parts of the soil, and whether roots branch more in wetter regions. Such examination will involve root excavations after various watering treatments in the field, plus laboratory investigation into the structural characteristics of roots that receive varied amounts of water. The water uptake characteristics of plant species with different root architectures will be compared. In particular, the investigators will examine roots of an agave with thick water-storing leaves and unbranched roots (Agave deserti), a grass with thin leaves and unbranched roots (Pleuraphis rigida), a cactus with thick stems and highly branched roots (Opuntia basilaris), and a small shrub with thin leaves and highly branched roots (Encelia farinosa). The species with thick leaves or stems can store much water and so may have different root responses in the early phases of drought than do those with thin leaves. Also, species with roots that can readily branch and thus proliferate in wetter regions of the soil will be compared with those with relatively unbranched roots. Water uptake ability per amount of root will be evaluated with respect to the variations in water due to depth in the soil and to seasonal differences such as time after rainfall and time during drought. This will help explain the present distribution of plants in deserts and whether changes in occurrence are expected in the future as climate changes. Changes in root properties of desert plants due to variations in soil moisture can also be used to predict plant responses in moister habitats where more extreme fluctuations in rainfall may occur in the future.